Field
The present invention relates to microelectromechanical systems and specifically to a closed loop drive circuitry for driving a MEMS resonator.
Description of the Related Art
Stable and low noise resonators are needed, for example, as primary (drive) resonators in vibratory MEMS gyroscopes. As the Coriolis force is directly proportional to the velocity of the driven resonator, the precision of its motion is essential. In an ideal case the drive loop, which realizes the oscillator, should keep the velocity of the drive resonator constant. As environmental variation always inflicts changes in the properties of the MEMS, constant velocity can only be approximated. A MEMS resonator is any small size device that can be made to vibrate at least at one resonant frequency or resonance mode by exciting it at the resonant frequency drive force.
Another parameter of interest is the speed at which the resonator attains the state of constant oscillation, i.e. start-up time. In a capacitively excited MEMS resonator, the available drive force is limited and therefore the frequency of oscillation is set by the main resonance mode of the element. This allows minimization of the required drive voltage. On the other hand, quick start-up typically refers to high drive force and high gain during start-up.